Holding the BKL in input_open_file seems pointless because it does not
protect against updates of input_table, and all open functions from the
underlying drivers have proper mutex locking.

This makes input_open_file take the input_mutex when accessing
the table and no lock when calling into the lower function.
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Acked-by: NThadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Signed-off-by: NDmitry Torokhov <dtor@mail.ru>